Gaseous electric discharge lamp device



April 1939- E. G. DORGELO ET AL 2,152,987

GASEOUS ELECTRIC DISCHARGE LAMP DEVICE Filed Nov. 16, 195i INVENTORSEduard, G. Dorgelo Willem Elenloaas Hendricus J. Lem ens ATTOR N EYPatented Apr. 4, 1939 UNITED STATES PATENT OFFICE Eduard G. Dorgelo,Willem Elenbaas, and Hen-v dricus J. Lemmens, assignors to GeneralEindhoven, Netherlands, Electric Company, a corporation of New YorkApplication November 16, 1937, Serial No."174,848 In Germany November2'7, 1936 2 Claims.

The present invention relates to gaseous electric discharge lamp devicesgenerally and more particularly the invention relates to mercury vapordischarge devices of the liquid cooled type 5 capable of operation withvapor pressures in the order of atmospheres. Devices of this type arenow known in the art and the structural details and operatingcharacteristics of such devices are described in co-pending applicationSerial Number 46,952, filed October 26, 1935.

Such liquid cooled devices consist of an elongated, tubular containerhaving a pair of solid electrodes sealed therein one at each end thereofwhich project a short distance, preferably less than about 5 mm., from aquantity of vaporizable metal, such as mercury or an amalgam, partlysurrounding the solid electrode. Due to the fact that the solidelectrodes project but a slight distance from the surroundingvaporizable metal 20 and the fact that the lamp device is cooled byliquid flowing over its exterior surface the heat generated at thesolidelectrodes during the operation of the device is conductedtherefrom to the liquid cooling medium where it is dissipated at suchrate that the temperature of the solid electrodes is kept below that atwhich a rapid deterioration thereof would take place. Such devices arecapable of operation with current loads of 400 watts per cm. of thedischarge path and higher and the arc discharge therein is constrictedby the high vapor pressure which is in the order of atmospheres. Whilesuch devices are successfully operated on alternating current it isfrequently desirable to operate this type of device on direct current.We have observed that when a lamp device of this type having electrodesof the same size and which is suitable for operation on alternatingcurrent is operated on direct current the life thereof is considerablyshorter than when the lamp device is operated on alternating current.

The object of the present invention is to provide a gaseous electricdischarge lamp device of the above type which is capable of operation ondirect current and which has a long useful operating life. Still furtherobjects and advantages attaching to the device and to its'use andoperation will be apparent to those skilled in the art from thefollowing particular description.

We have discovered that the cause of the dif- -ficulty is a more rapidvaporization of the mercury about the electrode serving as the anodethan of the mercury about the electrode serving as the cathode duringthe operation of the device due to the fact that the projecting part ofthe anode, which is the same size as the corresponding part of thecathode, is heated to a higher temperature by the discharge incident atthese electrodes. The quantity of mercury about the anode is reduced andless of the surface of the anode covered thereby. The conduction of heatfrom the anode through the mercury is reduced and the temperature of theanode increases to shorten the useful life thereof and of the lampdevice.

Having discovered the cause of the difficulty the solution thereof iscomparatively simple and we have solved the problem by enlarging theanode with respect to the cathode. Preferably the anode is 1.5 to timeslarger in cross section than the cathode. The increased size of theanode resultsin a lower voltage drop thereat and less heat is generatedthereat during the operation of the device. Further the larger size ofthe anode increases the dissipation of heat therefrom by conductionthrough the mercury to the cooling medium for the lamp device. The heatdissipated by radiation from the exposed part of the anode is alsoincreased due to the larger area of said part. The heat dissipated fromthe anode by conduction and convection through the vapor from themercuryabout the anode is increased by the increased area of the anode.The anode of a lamp device having this structure is not at too high atemperature during the operation of the device on direct current and thelamp device has a long useful operating life.

In the drawing accompanying and forming part of this specification anembodiment of the invention is shown in a side elevational, partlysectional view.

Referring to the drawing the gaseous electric discharge device comprisesan elongated tubular container l of vitreous material, such as quartz,having an insidediameter of about 2 mm. and an outside diameterof about4 mm. Two solid electrodes 2 and 3 consist of tungsten wire and aresealed into said container I, one at each end thereof. Said electrodes 2and 3 are prolongations of the tungsten current leads 4 and 5,respectively. When desired, a graded seal is interposed between thequartz container and the current leads 4 and 5. Said electrode 2 is thecathode and is about 600 microns in diameter.

' The diameter of the anode 3 is about 1006 microns. The cathode 2 isheated to an are discharge supporting temperature by the dischargeincidient thereat and, when desired, is coated or impregnated with anactivating material having high electron emissivity characteristics,such as an alkaline earth oxide. Said electrodes 2 and 3 are immersedfor the greater part of their length in a quantity of mercury 6 andproject therefrom a distance of about 0.5 to 1.5 mm. The container I hasa starting gas therein, such as argon, at a pressure of about 50 mm. atroom temperature. The distance between said electrodes 2 and 3 is about12.5 mm.

The gaseouselectric discharge lamp device is mounted in a cylindricalvessel 1 of vitreous material which is closed at both ends by stoppers 8and 9 of a material impervious to water, such as rubber. The currentleads in and H connected to the electrode leads! and 5, respectively, ofthe gaseous electric discharge device pass through said stoppers 8 and9, respectively. The current leads ID and I l are surrounded by tubes l2and I3, respectively, which consist of an electrically insulating, waterproof material, such as glass. The vessel 1 is provided with two tubes,one at each end thereof, so that a cooling fluid, such as water,

i may be passed through the vessel 1. The cooling equilibrium. The arewater passing over the surface of the gaseous electric discharge lampdevice conducts heat away from said lamp device to prevent thedevelopment of excessive temperatures in said lamp.

The discharge device is connected in series with a ballast resistance tothe'terminals of direct current source which has a voltage of about 600volts. The series resistance should permit a current of about 2 amperesto flow through the lamp device when the arc discharge therein is atoperating voltage between the electrodes is then about 500 volts whichcorresponds to a mercury vapor pressure of about atmospheres. Thecurrent load on the device is about 800 watts per cm. of length of thedischarge path.

The lamp device described above has a long useful operating life and iscapable of operation on direct current. It will be understood, ofcourse, that while the lamp unit is useful in the illuminating fieldgenerally and particularly for picture projection purposes it is alsouseful in therapeutic or hygienic work when the vessel fl consists ofamaterial which transmits the ultra violet rays emitted by the dischargedevice.

While we have shown and described and have pointed out in the annexedclaims certain novel features of the invention, it will be understoodthat various omissions, substitutions and changes in the forms anddetails of the device illustrated and in its use and operation may bemade by those skilled in the art without departing from the broad spiritand scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. A gaseous electric discharge lamp device of the high pressure typecomprising an elongated, tubular container having electrodes sealedtherein at each end thereof and a quantity of vaporizable metal partlysurrounding each of said electrodes, one of said electrodes being acathode and the other of said electrodes being an anode, the part ofsaid anode projecting from said vaporizable metal being 1.5 to 5 timeslarger in cross section than the corresponding part of said cathode toprevent excessive temperatures thereat during the operation of thedevice.

2. A gaseous electric discharge lamp device of the high pressure typecomprising an elongated, tubular container having electrodes sealedtherein at each end thereof and a quantity of vaporizable metal partlysurrounding each of said electrodes, said electrodes projecting adistance of about 0.5 to 1.5 mm. beyond said vaporizable metal, one ofsaid electrodes being a cathode and the other of said electrodes beingan anode, the part of said anode projecting from said vaporizable metalbeing 1.5 to 5 times larger in cross section than the corresponding partof said cathode to prevent excessive temperatures thereat during theoperation of the device.

EDUARD G. DORGELO. WILLEM ELENBAAS. HEN'DRICUS J. LEMMENS.

